In U.S. Pat. No. 3,752,877, for example, there is described a process for the reduction of compounds, such as sulfur, nitrogen oxides, and the like, occurring in industrial gases, such as the tail gases from Claus plant, or the like. In the patented process, the tail gases are first heated to an elevated temperature by a conventional burner through a heat exchanger that prevents mixing of the products of combustion with the tail gases. After heating, the tail gases are mixed with a reducing gas containing hydrogen and carbon monoxide. The reducing gas is produced by burning air and fuel in the presence of steam in a sub-stoichiometric combustion reaction. When hydrocarbon is burned stoichiometrically or sub-stoichiometrically, it is difficult to avoid formation of free carbon or soot, which is harmful to subsequent process steps. It is also difficult to insure complete consumption of free oxygen, which of course is not wanted in the reducing gas.